Biomedical subjects

Siew Hong Lam

Publications and source records attributed to Siew Hong Lam.

6 recordsLinked to original sources

PubMed2006

Transcriptome kinetics of arsenic-induced adaptive response in zebrafish liver.

Arsenic is a prominent environmental toxicant and carcinogen; however, its molecular mechanism of toxicity and carcinogenicity remains poorly understood. In this study, we performed microarray-based expression profiling on liver of zebrafish exposed to 15 parts/million (ppm) arsenic [As(V)] for 8-96 h to identify global transcriptional changes and biological networks involved in arsenic-induced adaptive responses in vivo. We found that there was an increase of transcriptional activity associated with metabolism, especially for biosyntheses, membrane transporter activities, cytoplasm, and endoplasmic reticulum in the 96 h of arsenic treatment, while transcriptional programs for proteins in catabolism, energy derivation, and stress response remained active throughout the arsenic treatment. Many differentially expressed genes encoding proteins involved in heat shock proteins, DNA damage/repair, antioxidant activity, hypoxia induction, iron homeostasis, arsenic metabolism, and ubiquitin-dependent protein degradation were identified, suggesting strongly that DNA and protein damage as a result of arsenic metabolism and oxidative stress caused major cellular injury. These findings were comparable with those reported in mammalian systems, suggesting that the zebrafish liver coupled with the available microarray technology present an excellent in vivo toxicogenomic model for investigating arsenic toxicity. We proposed an in vivo, acute arsenic-induced adaptive response model of the zebrafish liver illustrating the relevance of many transcriptional activities that provide both global and specific information of a coordinated adaptive response to arsenic in the liver.

Adaptation, Physiological↗

PubMed2006

Modeling liver cancer using zebrafish: a comparative oncogenomics approach.

Although the zebrafish has many attributes of a promising cancer model, one outstanding question is how similar zebrafish and human tumors are at the molecular level. To date, supporting data from histology and 'gene-to-gene' comparisons with human data offer limited insights. Using comparative microarray analyses, we found striking molecular similarities between zebrafish and human liver neoplasia. Our data indicate that zebrafish liver tumors possess the general molecular hallmarks of human liver cancer and some of the molecular similarities extend to the progression of liver tumors. The molecular conservation between fish and human liver tumors underscored the strong association and fundamental importance of these genes in liver neoplasia as well as their clinical potentials as diagnostic markers and/or therapeutic targets. In addition, our comparative oncogenomic work provides a general framework for comparing and validating microarray data of zebrafish model with human cancer, thus adding confidence of using the zebrafish to model human cancers.

Animals↗

PubMed2005

Conservation of gene expression signatures between zebrafish and human liver tumors and tumor progression.

The zebrafish (Danio rerio) has been long advocated as a model for cancer research, but little is known about the real molecular similarities between zebrafish and human tumors. Comparative analysis of microarray data from zebrafish liver tumors with those from four human tumor types revealed molecular conservation at various levels between fish and human tumors. This approach provides a useful strategy for identifying an expression signature that is strongly associated with a disease phenotype.

Amino Acid Sequence↗

PubMed2005

Development of estrogen-responsive transgenic medaka for environmental monitoring of endocrine disrupters.

To develop a transgenic fish system to monitor environmental pollution, we generated a mvtg1:gfp transgenic medaka line, in which the gfp reporter gene was under the control of medaka vitellogenin1 (mvtg1) gene promoter. In this transgenic line, GFP was exclusively expressed in the liver of the mature adult female. Male and juvenile transgenic fish did not express GFP but could be induced to express GFP in the liver after exposure to 17-beta-estradiol (E2). Concurrent accumulation of mvtg1 and gfp mRNAs was observed during both development and estrogen treatment, indicating that the gfp transgene was faithfully expressed under the mvtg1 promoter. Dose- and time-dependent induction of GFP expression by E2 was investigated in male transgenic fish. The lowest-observed-effect concentration (LOEC) of E2 to induce GFP expression was 0.5 microg/L by observation of live fish and 0.05-0.1 microg/L by observation of dissection-exposed liver in a 30 day exposure experiment. GFP expression was observed within 36 h after treatment in high concentrations of E2 (5 microg/L), and it took longer to detect GFP expression under lower concentrations of E2. By removal and readdition of E2, we demonstrated that GFP expression was repeatedly induced. Finally, we also demonstrated that GFP expression could be induced by other estrogenic compounds, including 17-alpha-ethynylestradiol (EE2, 0.05 microg/L), diethylstibestrol (DES, 5 microg/L), estriol (10 microg/ L), and bisphenol A (BPA, 1 mg/L), but not by weak estrogenic chemicals such as nonylphenol (NP, up to 1 mg/ L) and methoxychlor (MXC, up to 20 microg/L). Our experiments indicated the broad application of the transgenic line to monitor a wide range of estrogenic chemicals.

Animals↗

PubMed2005

Transcriptome analysis of zebrafish embryogenesis using microarrays.

Zebrafish (Danio rerio) is a well-recognized model for the study of vertebrate developmental genetics, yet at the same time little is known about the transcriptional events that underlie zebrafish embryogenesis. Here we have employed microarray analysis to study the temporal activity of developmentally regulated genes during zebrafish embryogenesis. Transcriptome analysis at 12 different embryonic time points covering five different developmental stages (maternal, blastula, gastrula, segmentation, and pharyngula) revealed a highly dynamic transcriptional profile. Hierarchical clustering, stage-specific clustering, and algorithms to detect onset and peak of gene expression revealed clearly demarcated transcript clusters with maximum gene activity at distinct developmental stages as well as co-regulated expression of gene groups involved in dedicated functions such as organogenesis. Our study also revealed a previously unidentified cohort of genes that are transcribed prior to the mid-blastula transition, a time point earlier than when the zygotic genome was traditionally thought to become active. Here we provide, for the first time to our knowledge, a comprehensive list of developmentally regulated zebrafish genes and their expression profiles during embryogenesis, including novel information on the temporal expression of several thousand previously uncharacterized genes. The expression data generated from this study are accessible to all interested scientists from our institute resource database (http://giscompute.gis.a-star.edu.sg/~govind/zebrafish/data_download.html).

Journal Article↗

PubMed2004

Molecular cloning of zebrafish and medaka vitellogenin genes and comparison of their expression in response to 17beta-estradiol.

In the present study, both zebrafish and medaka vitellogenin genes have been isolated and used as a biomarker to compare the two small aquarium fish in response to estrogen treatment and thus to evaluate the two fish models in development of a biomonitoring system for environmental estrogens. The isolated zebrafish vitellogenin gene, zvtg1, is the most abundantly expressed vitellogenin gene in zebrafish and its complete protein sequence of 1360 amino acids was deduced from a genomic and a cDNA clone. The isolated medaka vitellogenin (mvtg1) genomic clone covers 1053 amino acids in the N-terminal. Both zebrafish zvtg1 and medaka mvtg1 are specifically expressed in female liver and their expression can be induced by 17beta-estradiol (E2) in male fish both by intramuscular injection and immersion treatment. A real-time reverse transcriptase polymerase chain reaction (RT-PCR) assay was developed for quantification of vitellogenin mRNA level in both control fish and E2-treated fish. The lowest-observed-effect concentrations of E2 for the induction of vitellogenin mRNAs were observed at 1 microg/l for zebrafish and 0.1 microg/l for medaka in a 2-day exposure experiment. Further kinetics studies of the two fish models indicated that medaka was able to respond much faster to E2 treatment than zebrafish, while the zebrafish can attain a much higher level of vitellogenin mRNAs than medaka after a long-term E2 treatment. The implication of these observations may be that the medaka system is better in monitoring acute treatment while the zebrafish system is better in monitoring chronic exposure.

Amino Acid Sequence↗